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What does the Fixed Frame mean in rviz?

asked 2014-11-19 06:59:24 -0500

somebodyus gravatar image

What does the Fixed Frame mean in rviz?

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answered 2014-11-19 07:42:06 -0500

Tom Moore gravatar image

updated 2018-02-19 07:49:29 -0500

It's the tf frame that all positions/measurements that you see are relative to. For example, let's say you have a robot that has two frames, odom (a world-fixed frame) and base_link (the body frame of the robot). The robot is at position (10, 0) with a heading of pi/2 in the odom frame, and it has a LIDAR on board that sees an obstacle 5 meters directly in front of it. If you set your Fixed Frame to odom, that obstacle will appear at position (10, 5). If you set your Fixed Frame to base_link, it will appear at (5, 0).

EDIT: updating answer for comment from @malharjajoo

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Thank you so much.

Does the Grid always be the world coordinate? If I set /odom as the fixed frame. Rviz will draw obstacle at potions (10, 5) in the Grid?

I think the heading in your assumption should be pi/2.

somebodyus gravatar image somebodyus  ( 2014-11-19 08:01:15 -0500 )edit

Yeah, fixed that, sorry. Need coffee.

And yes, if you set the fixed frame to /odom, the obstacle will be drawn at (10, 5).

Tom Moore gravatar image Tom Moore  ( 2014-11-19 08:11:31 -0500 )edit

@tom, I didn;t really follow your explanation, what does heading = pi/2 mean ( is the robot facing left by 90 degree compared to lidar) ?

also could you elaborate how the (10,0) and (10,5) works out ? can't seem to visualize that based on the explanation.

malharjajoo gravatar image malharjajoo  ( 2018-02-07 16:55:00 -0500 )edit

What happens If I keep my fixed_frame as /map instead of /odom and /base_link frame?

Nagarjun gravatar image Nagarjun  ( 2020-10-14 17:16:58 -0500 )edit

Then you will see everything displayed in the map frame. In my drawing, just imagine another coordinate frame like the odom frame, but not with the same origin/position.

All the fixed frame does is define where the origin is when rviz displays things.

Tom Moore gravatar image Tom Moore  ( 2020-10-19 03:20:39 -0500 )edit

I'll just write what I understood from this, let me know if I'm wrong. So the map frame is linked to the environment and the odom frame is linked to the starting point of the robot on the map.

Anshul gravatar image Anshul  ( 2021-04-23 17:03:09 -0500 )edit

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Asked: 2014-11-19 06:59:24 -0500

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Last updated: Feb 19 '18